The aim of this research is to maximize fluorapatite formation in enamel from topical application of aqueous solutions of sodium monofluorophosphate and sodium fluoride. In the past year, we explored the effects of solution concentration, pH, application time, and acidic pretreatment of the enamel. Fluoride from sodium fluoride solutions penetrated more easily into the enamel than monofluorophosphate solutions under similar conditions. The former also produced more apatitically bound fluoride than the latter if an incubation period was allowed to follow the treatment, or if a prolonged application time was permitted. A monofluorophosphate solution was more efficient in effecting fluoride penetration and fluorapatite formation than a solution that contained the same amount of fluoride ion but no monofluorophosphate. Thus, the effect of monofluorophosphate interactions with enamel could not be explained solely as an action of the ionic fluoride present in the solution. Neutral and acidic sodium fluoride solutions buffered with phosphate or acetate gave much better results with respect to fluoride penetration and the amount of apatitically bound fluoride formed in depth as a result of a prolonged treatment time than did the monofluorophosphate solutions. Work for the coming year will attempt to determine if effects of specific buffers are important for achieving high yields of apatitically bound fluoride, or, simply if maintenance of a stable pH can explain the findings. Other experiments will be concerned with surface active agents and their influence on the speed of fluoride interactions in depth as well as on the quantity and quality of reaction products. Finally, it is planned to explore the use of varnishes as potential sealants. Varnishes may function as diffusion barriers, thus enabling prolonged fluoride-enamel interaction and/or incubation period directly after treatment.